Collymore contacted police to complain that he had received racist comments. A man has appeared in court and denied the charge.

Simon Hyacinth, joint-co-ordinator of anti-racism charity Football Unites, Racism Divides, said in the past fans might have voiced their anger at a player among friends, but now they were able to air their views online.

He said: "The way Facebook and Twitter is used is a concern, as people voice their feelings as and when they happen, rather than taking stock.

"The problem for me is you've got an avenue there to voice feelings as soon as they emerge. Previously, you'd speak to friends and could get rid of your anger in a relatively safe environment. Once it's online on Facebook or Twitter it's there as evidence and even if you regret it, it's too late."

Dr Chris Brauer, senior lecturer in the Department of Computing at Goldsmiths University of London, told BBC Breakfast Twitter gave celebrities like footballers a "unique opportunity" to communicate directly with fans.

However, he said some fans used abuse to try to get celebrities to respond to them.

"They've been very successful because celebrities have retweeted them and engage with these people which encourages more people [to be abusive]," Dr Brauer said.

He said while abuse had traditionally come from a handful of internet "trolls", recent studies had seen people were getting more organised and encouraging others to join in with online abuse.

He said: "It's going to move from rogue elements to an organised movement to ruin people's reputation."

You can't get away with it on the football pitch but on Twitter you seem to be able to say what you want to anyoneLizzie Cundy, Ex-wife of former footballer

He added that while it was best to ignore abuse, it did not always solve the problem.

Earlier this month it was reported Manchester City defender Micah Richards left Twitter after being the victim of racist abuse.

Dr Brauer said: "For days and days an enormous amount of abuse was hurled at him. You can leave the room but that doesn't mean people stop talking."

Last month the Football Association issued a reminder encouraging those involved in football themselves to think about what they posted on Twitter.

An FA spokesman said: "Following a recent increase in the number of complaints and referrals it has received in relation to postings on Twitter the FA sought to remind all participants in January that they are required to act in the best interest of the game at all times and should be aware that their postings on social networking sites are likely to be subject to public and media scrutiny."

Lizzie Cundy, the ex-wife of former Chelsea player Jason Cundy, said she had received abuse on Twitter when her marriage ended.

She said: "I had some very abusive tweets about my family. I can take stick, I don't mind a few jokes but I think sometimes it goes too far.

"I really do feel Twitter should be monitored. You can't get away with it on the football pitch but on Twitter you seem to be able to say what you want to anyone."

She said it was difficult to ignore abuse, particularly as she then worried the person posting the comments would start to abuse someone else.

But she said Twitter did have its plus points as long as people were careful.

"You can see your idol and what they're up to. It's fantastic," she said.